The present invention generally relates to semiconductor devices and methods of producing semiconductor devices, and more particularly to a semiconductor device in which a semiconductor element is sealed by a resin package and a method of producing such a semiconductor device.
As will be described later in conjunction with drawings, a conventional semiconductor device comprises a stage, a semiconductor element mounted on the stage, a pair of stage bars extending from both sides of the stage for supporting the stage during the production process, leads, wires connecting terminals of the semiconductor element with the corresponding leads, and a generally flat parallelepiped resin package for sealing the semiconductor element and its surrounding parts.
The pair of stage bars extend up to respective side surfaces of the resin package. In other words, free tip ends of the stage bars are exposed at the respective side surfaces of the resin package. This is because the stage bars are essential to support the stage during the production process, and the excess length of the stage bars are cut along the side surfaces of the resin package only during one of the final production processes. However, since the free tip ends of the stage bars are exposed at the side surfaces of the resin package, external moisture can enter the semiconductor device from a gap formed between the resin package and the free tip ends of the stage bars. This moisture will enter inside the semiconductor device along the stage bars and will eventually reach the semiconductor element because the stage bars are connected to the stage which is mounted with the semiconductor element. When the moisture reaches the semiconductor element, the operation characteristic of the semiconductor device becomes deteriorated and causes breakdown of the semiconductor device.
Therefore, although the stage bars are essential in supporting the stage during the production process, there are problems in that the stage bars of the completed semiconductor device lead the external moisture to the semiconductor element and the conventional semiconductor device is insufficiently sealed against moisture.
Accordingly, various semiconductor devices have been proposed in which the stage bars are cut during the production process so that the free tip ends of the stage bars do not extend up to the side surfaces of the resin package. For example, in the semiconductor device proposed in a Japanese Laid-Open Patent Application No. 58-161349, a frame-shaped adhesive tape is adhered on the leads and the stage bars before the free tip ends of the stage bars are cut, so as to provide a support for the stage during the remaining production processes. In the semiconductor devices proposed in Japanese Laid-Open Patent Applications No. 58-191457 and No. 60-46058, an adhesive tape is adhered on each stage bar and the leads adjacent thereto before the free tip ends of the stage bars are cut, so as to provide a support for the stage during the remaining production processes.
Since the tip ends of the stage bars are not exposed at the side surfaces of the resin package, there is no possibility of the external moisture entering the semiconductor device from the side surfaces of the resin package. However, according to these previously proposed semiconductor devices using the adhesive tape, the adhesive tape remains inside the resin package of the completed semiconductor device. Generally, it is extremely difficult to obtain a satisfactory adhesion between the adhesive tape and the stage bars and the leads. For this reason, when the moisture enters from a gap formed between one of the leads and the resin package, the moisture is prevented from reaching the semiconductor element directly because the leads are not connected to the stage, but the moisture will advance along a gap formed between the lead and the adhesive tape adhered thereon, due to the poor adhesion therebetween. The moisture advancing along the gap between the lead and the adhesive tape will then reach a gap between the stage bar and the adhesive tape adhered thereon. As a result, the moisture will eventually reach the semiconductor element by way of the stage bar. Therefore, these previously proposed semiconductor devices are also insufficiently sealed against moisture.
On the other hand, in another semiconductor device proposed in Japanese Laid-Open Patent Application No. 58-197864, the free tip ends of the stage bars exposed at the side surfaces of the resin package are covered by a suitable material so as to prevent the external moisture from entering the semiconductor device from the side surfaces of the resin package where the free tip ends of the stage bars are exposed. However, it is difficult to find a suitable material that would satisfactorily adhere on the side surfaces of the resin package and provide a satisfactory seal. Furthermore, since the material covers only portions of the side surfaces of the resin package where the free tip ends of the stage bars are exposed, the sealing provided thereby against the external moisture is incomplete.